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<title> Transaction support </title><link rel="stylesheet" href="styles.css" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/styles.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets Vimages/callouts/"><link rel="home" href="index.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/index.html" title="JBoss 3.0 Documentation"><link rel="up" href="ch12.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch12.html" title="Chapter 12. Container architecture - design notes"><link rel="previous" href="ch12s31.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch12s31.html" title="Container"><link rel="next" href="ch12s68.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch12s68.html" title="Security"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><table border="0" cellpadding="0" cellspacing="0" height="65"><tr height="65"><td rowspan="2"><img src="jboss.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/jboss.gif" border="0"></td><td rowspan="2" background="gbar.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/gbar.gif" width="100%" align="right" valign="top"><a href="index.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/index.html"><img src="doc.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/doc.gif" border="0"></a><a href="ch12.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch12.html"><img src="toc.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/toc.gif" border="0"></a><a href="ch12s31.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch12s31.html"><img src="prev.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/prev.gif" border="0"></a><a href="ch12s68.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch12s68.html"><img src="next.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/next.gif" border="0"></a></td></tr><tr></tr></table><div class="section"><a name="d0e8614"></a><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="d0e8614"></a> Transaction support </h2></div></div><div class="section"><a name="d0e8617"></a><div class="titlepage"><div><h3 class="title"><a name="d0e8617"></a>Background</h3></div></div><p>In the world of distributed transaction processing (DTP) a series of
specifications developed by OpenGroup
(www.opengroup.org) represent the most widely adopted DTP model. </p><p>Opengroup specifications define major components participating in the
DTP
model as well as a set of APIs
that define communication between these components. Components
participating in the DTP model are:
application programs, resource managers, and a transaction manager. The
interface
defined between application
programs wishing to participate in global trasactions and the transaction
manager is called the TX
interface, while the interface between transaction managers and the resource
managers is called the XA interface.</p><p>Sun Microsystems Inc followed this DTP model and as part of J2EE
introduced the Java Transaction Service (JTS)
and the Java Transaction API (JTA) specifications.</p></div><div class="section"><a name="d0e8626"></a><div class="titlepage"><div><h3 class="title"><a name="d0e8626"></a>JTS and JTA</h3></div></div><p>The difference between JTS and JTA is often a source of confusion.
Simply
put JTS defines above mentioned components
participating in the DTP model, while JTA captures interfaces between
them.</p><p>JTS defines five major players in the DTP model of Java Enterprise
middleware:</p><p>Transaction Manager as a core component which provides services of
transaction resource management ( i.e resource
enlistment, delistment), transaction demarcation, synchronization notification
callbacks, trasaction context
propagation and two-phase commit initiation and recovery coordination with
resource managers.</p><p>The application server provides infrastructure required to support the
application run-time environment.</p><p>A resource manager is a component that manages access to a persistent
stable storage system. Each resource manager cooperates with a
Transaction Manager in two-phase commit intiation and failure recovery. An
example of resource manager would be
database driver.</p><p>EJB's can either use declarative transaction management specified in
the ejb-jar.jar xml descriptor, or programmatic transaction manager
using the <tt>UserTransaction</tt> interface. Either way, the
transaction services are provided by the application server.</p><p>A communication resource manager supports transactional context
propagation. Simply put this component allows
the transaction manager to participate in transactions initiated by other
transaction managers. JTS does not
specify a protocol for this component.</p></div><div class="section"><a name="d0e8646"></a><div class="titlepage"><div><h3 class="title"><a name="d0e8646"></a>Core implementation</h3></div></div><p>Jboss includes it's support of JTS and JTA specifications in the
jboss.tm package. This package include implementation of
TransactionManager , Transaction, Xid and Synchronization from JTA
specification. </p><p>However, the key class is TxCapsule. TxCapsule is has a very
abstract notion but it closely matches the idea of
transaction context. Transaction context in turn is best thought of as a
state of all transactional operations on the
participating resources that make up one global transaction . Therefore
transactional context, or in Jboss's case
TxCapsule, captures all participating XaResources and their states, all
particiating threads as well as a global Xid
identifying global transaction.</p><p>TxCapsule provides the real meat. It enables enlisting and delisting
of transactional resources, importing of
transactions into capsule, provides creational point and access to Xid of the
current global transaction, calls
Synchronization callback but most importantly it initiates the two-phase commit
protocol as well as rollback mechanisms
defined by the two-phase commit protocol.</p><p>TransactionImpl implements Transaction interface from JTA. Each
transaction is a part of TxCapsule which in turn can
"host" transactions representing the TxCapsule. All of TransactionImpl methods
are basically indirection calls to the hosting
TxCapsule. </p><p>TxManager implements TransactionManager interface defined in JTA. As
you might have guessed by now, it controls the lifecycle of all
TxCapsules. Since TxCapsule is a relatively heavyweight object, capsules
are recycled in a soft reference queue.</p></div><div class="section"><a name="d0e8659"></a><div class="titlepage"><div><h3 class="title"><a name="d0e8659"></a>TxInterceptor</h3></div></div><p>Following the previously introduced interceptor framework JBoss
introduces two transactional interceptors TXIntereceptorBMT
and TXIntereceptorCMT. Both interceptors closely interact with TxManager in
order to achieve proper transactional semantics.</p><p>TXIntereceptorBMT provides an instance of UserTransaction to the right
transactional context. TxInterceptorBMT is used
in the case of user demarcated, i.e explicit transactional management. For
more information on details of semantics
refer to p174 of EJB1.1 spec.</p><p>TxInterceptorCMT moves all transactional management work to the
container. Depending on the transaction attributes specified in th
ejb-jar.xml file
(i.e TX_REQUIRED, TX_SUPPORTS, TX_REQUIRES_NEW etc) the container decides how
to manage
the transactional context of the invoked call.</p></div></div><table border="0" cellpadding="0" cellspacing="0" height="65"><tr height="65"><td rowspan="2"><img src="gbar.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/gbar.gif" width="432" height="79"></td><td rowspan="2" background="gbar.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/gbar.gif" width="100%" align="right" valign="top"><a href="index.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/index.html"><img src="doc.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/doc.gif" border="0"></a><a href="ch12.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch12.html"><img src="toc.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/toc.gif" border="0"></a><a href="ch12s31.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch12s31.html"><img src="prev.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/prev.gif" border="0"></a><a href="ch12s68.html" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/ch12s68.html"><img src="next.gif" tppabs="http://www.huihoo.org/jboss/online_manual/3.0/next.gif" border="0"></a></td></tr><tr></tr></table></body></html>⌨️ 快捷键说明
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